Accelerating Rate Calorimeter (ARC) for Chemical Reactivity Testing
An Accelerating Rate Calorimeter (ARC®) is a high-sensitivity adiabatic calorimeter used to study the thermal stability, decomposition behavior, and self-heating potential of chemical substances—especially under unstable or runaway reaction conditions. The ARC is designed to simulate and analyze worst-case thermal scenarios by mimicking adiabatic conditions. It’s used primarily for hazard assessment of materials in chemical, pharmaceutical, battery, and energy industries.
ARC provides pressure and temperature response when sample is subjected to heat. It is used to obtain thermodynamic properties of chemical reactions:
- Number of exotherms
- Onset temperature of exotherm
- Temperature and pressure rise rate
- Total pressure and volume of gases
- Adiabatic temperature rise (ΔTad)
- Time to maximum rate (TMR)
- Activation energy (Ea)
- Heat of reaction or decomposition (Heat generated)
Exotherm rates as low as 0.02°C/min can be detected under heat-wait-search heating mode, or as low as 0.005°C/min for iso-aging mode. The significant advantage that the ARC offers over other similar techniques is exothermic onset detectability at 0.02°C/min along with simultaneous pressure measurement.
Standards / References:
ASTM E1981 “Assessing Thermal Stability of Materials by Methods of Accelerating Rate Calorimetry”
Equipment used:
- CSI ARC 2000
- TIAX (Netzsch Instrument) ARC 254
Columbia Scientific Inc’s (CSI) Accelerating Rate Calorimeter (ARC) 2000
TIAX ARC 254
Example Plot:
Sample Temperature & Pressure vs. Time
Temperature rise rate & Pressure rise rate vs. Time
Table 1: ARC Test result
| Cell Type | Wt. Loss | Onset T of Exotherm* | Max. Holder T | Max. Cell T | Heat of Reaction | Max. Cell dT/dt | Max. Cell Holder dT/dt | Cell V Drop T | Cell T at 15 °C/min |
|---|---|---|---|---|---|---|---|---|---|
| Typical | % | °C | °C | °C | kJ | °C/min | °C/min | °C | °C |
| 21700 | 66 | 90 | 434 | 1352 | 81 | 29,292 | 627 | 106.2 | 171.4 |
FAQ:
1. How does Accelerating Rate Calorimeter (ARC) work?
- Sample placement: The test cell (battery, chemical, powder, etc.) is placed inside a sealed container call test cell.
- Heating: most common heating mode is Heat-Wait-Search; Heat calorimeter to target temperature (heat step of 5-10˚C) → Wait to equilibrate temperature of sample, holder and calorimeter → Search for detecting exotherm.
- If no self-heating, continue next heat step.
- If self-heating is detected, the ARC switches to adiabatic tracking mode, where furnace heats same rate as sample.
- Runaway capture: If thermal runaway occurs, the ARC measures temperature and pressure with respect to time.
2. Can we measure amount of heat and gas generated during thermal runaway?
Yes, ARC measures sample temperature and pressure with respect to time under adiabatic conditions. Adiabatic temperature rise is estimated by temperature rise times thermal inertia. Heat generated is estimated by the following:
Q (joules) = Msample (g) x Cpsample(Joules/g.C) x Adiabatic T rise of sample (°C)
ARC continuously measures the pressure inside the sample container. From the know fixed volume of container and pressure, volume of gas generated is estimated
3. What types of materials can be tested using ARC?
ARC testing can be performed on a wide range of substances, including:
- Reactive organic and inorganic chemicals
- Polymerization systems and curing agents
- Catalyst mixtures
- Battery components (electrolytes, electrodes, separators)
- Energetic materials and propellants
4. What information does the ARC test provide for process safety
It provides critical thermal and kinetic data that is essential for ensuring process safety:
- Safe operating temperature and pressure
- Emergency relief system design (e.g., DIERS/PSV sizing)
- Reaction hazard classification (exothermicity, runaway potential)
5. How is ARC data used in reactive chemical risk assessment?
It is used in the following ways:
- Identifying thermal instability and reaction hazard
- Evaluating thermal runaway potential
- Designing pressure relief and vent systems
- Defining safe operating and storage conditions
- Determining self-accelerating decomposition temperature (SADT)
- Input for reaction kinetic modeling
- Supporting layer of protection analysis (LOPA)
6. How does ARC differ from DSC testing?
While Differential Scanning Calorimetry (DSC) provide screening data at small sample scales, ARC replicates adiabatic conditions to simulate real-world runaway behavior — offering more accurate insight into large-scale hazards.